As one of resistance change type memories, there is a Magnetic Random Access Memory (MRAM). MRAM writing schemes include a magnetic field writing scheme and a spin injection writing scheme. Of those writing schemes, the spin injection writing scheme has a characteristic that the smaller the size of a magnetic material, the smaller the spin injection current required for magnetization reversal, and thus is advantageous in terms of achieving high integration, low power consumption, and high performance.
An MTJ (Magnetic Tunnel Junction) element of the spin injection writing scheme has a stacked structure including two ferromagnetic layers and a non-magnetic barrier layer (insulating thin film) sandwiched therebetween, and stores digital data according to a change in magnetic reluctance caused by spin-polarized tunneling effect. The MTJ element can take a low resistance state and a high resistance state according to the magnetization alignment of the two ferromagnetic layers. When the magnetization alignment of the two ferromagnetic layers are in a parallel state (P state), the MTJ element is placed in a low resistance state, and when the magnetization alignment of the two ferromagnetic layers are in an anti-parallel state (AP state), the MTJ element is placed in a high resistance state.
When a P state is written, there is a need to allow a current required to reverse the MTJ element from an AP state to a P state to flow. When an AP state is written, there is a need to allow a current required to reverse the MTJ element from a P state to an AP state to flow.
Normally, MTJ elements, cell transistors, etc., have resistance distribution (variation). Thus, even in the case of the highest sum total of the resistances of an MTJ element and a cell transistor and parasitic resistances, there is a need to allow a sufficient write current to flow through the MTJ element so that data writing can be securely performed.
However, if the MTJ element, the cell transistor, etc., are designed to thus allow a sufficient write current to flow, then when conversely the resistance of the MTJ element, the resistance of the cell transistor, parasitic resistances, etc., are lowest, a current is too large, which may break down a barrier layer of the MTJ element. In this case, an excessive current which flows through the barrier layer of the MTJ element and accordingly the barrier layer may break down. This leads to a problem of deterioration in the reliability of the MTJ element.